Stylish. Something that fits the lady's face. Length isn't what matters.
In fact, I'm sometimes disappointed when I see a lady's photos with beautiful, long hair, then I arrive and she has it pulled straight back in a ponytail, or up in a tight bun. I get the practicality of that in a hobby setting (having to constantly pull hair away during certain activities), but that sometimes detracts from the overall presentation, at least to me.
It's interesting that you pose the question, though. I've been noticing more the number of ladies with long hair who don't let it hang loose during a session. That's why I say it may be worth considering cutting it shorter if you find yourself tying it back/up all the time.